TubaBum wrote:Looks like they are even more popular than some of the common custom ones you see on this website. I guess the simplest idea in mouthpiece technology is always the best.
Nah, all equally simple. A large part of the problem is that buyers have no reliable way to select the mouthpiece that will suit them best, so they tend to rely on word of mouth. That naturally tends to inflate the value of something like the Mt Vernon era Bachs, without doing a thing for highly available models that are apparently identical such as the Faxx line. For most people, while the mouthpiece makes a difference, once you get within the general ballpark it's really possible to do pretty well with whatever you have, so there's an element of self-fulfilling prophecy - you spend $250 for a mouthpiece and you're going to love it to death, and you'll go on to reinforce that word of mouth reputation.
In a situation like yours, the magic won't work, assuming your intonation really depends on actual specific physical parameters of the mouthpiece. Some Mt Vernon 18 online might have those parameters, but I don't think you know that for a fact, so without a chance to play it against that tuner, its value to you is not what it is to others.